Personalized therapeutics and companion diagnostics: a new paradigm in testing and treatment.

Serum contains 1-transferrin, and CSF contains 1 and 2 transferrins. The 2-transferrin in CSF is desialylated because of the presence of neuraminidase in the central nervous system. Hence, 2-transferrin is used as a marker of CSF leakage (1 ). Because 1-transferrin was present in serum but absent in drainage fluid, additional neuraminidase activity was suspected. This suspicion was supported by the culture of Staphylococcus aureus from the fluid. Most S. aureus strains have neuraminidase activity (2 ), and sepsis is associated with decreased sialylation of circulating transferrin (3 ).